Re: [RFC 1/4] drivers/nvdimm: Add perf interface to expose nvdimm performance stats

[Peter Zijlstra]

On Wed, May 12, 2021 at 10:08:21PM +0530, Kajol Jain wrote:
> +static void nvdimm_pmu_read(struct perf_event *event)
> +{
> +	struct nvdimm_pmu *nd_pmu = to_nvdimm_pmu(event->pmu);
> +
> +	/* jump to arch/platform specific callbacks if any */
> +	if (nd_pmu && nd_pmu->read)
> +		nd_pmu->read(event, nd_pmu->dev);
> +}
> +
> +static void nvdimm_pmu_del(struct perf_event *event, int flags)
> +{
> +	struct nvdimm_pmu *nd_pmu = to_nvdimm_pmu(event->pmu);
> +
> +	/* jump to arch/platform specific callbacks if any */
> +	if (nd_pmu && nd_pmu->del)
> +		nd_pmu->del(event, flags, nd_pmu->dev);
> +}
> +
> +static int nvdimm_pmu_add(struct perf_event *event, int flags)
> +{
> +	struct nvdimm_pmu *nd_pmu = to_nvdimm_pmu(event->pmu);
> +
> +	if (flags & PERF_EF_START)
> +		/* jump to arch/platform specific callbacks if any */
> +		if (nd_pmu && nd_pmu->add)
> +			return nd_pmu->add(event, flags, nd_pmu->dev);
> +	return 0;
> +}

What's the value add here? Why can't you directly set driver pointers? I
also don't really believe ->{add,del,read} can be optional and still
have a sane driver.